Device for dampening the oscillation of the arm of a handling equipment of the swingable lever type

ABSTRACT

A handling equipment of the swingable lever type comprises a driving double acting cylinder ( 5 ) having a chamber ( 18 ) in which a main piston ( 15 ) is sealingly mounted, which is slidable as a result of the selective delivery of fluid under pressure from opposite zones of the chamber ( 18 ) of the cylinder ( 5 ). The main piston ( 15 ) is connected to a rod ( 10 ) having a driving end ( 10   a ) which projects from the cylinder ( 5 ) and is associated with a movable arm ( 7 ). The equipment ( 1 ) is provided with a device for dampening the oscillation of the arm ( 7 ), which comprises an axial cavity ( 27 ) formed in the rod ( 10 ) and containing a service fluid. A stem ( 30 ) rigidly connected to the cylinder ( 5 ) and provided with at least one orifice ( 31, 31   a ) for the service fluid is sealingly and slidably mounted in the cavity ( 27 ), so that the movement of the rod ( 10 ) with respect to the stem ( 30 ) is slowed down as a consequence of the flowing of the service fluid through said orifice ( 31, 31   a ), if the sliding speed of the main piston ( 15 ) inside the cylinder ( 5 ) exceeds a threshold speed set by the cross-section of said orifice ( 31, 31   a ).

[0001] The present invention refers in general to handling equipments ofthe so-called swingable lever type.

[0002] More particularly, the invention relates to a device fordampening the oscillation of the arm of a handling equipment of theswingable lever type, which equipment comprises a driving double actingcylinder having a chamber in which a main piston is sealingly mounted,which is slidable as a result of the selective delivery of fluid underpressure at opposite zones of the chamber of the cylinder, the mainpiston being connected to a rod having a driving end which projects fromthe cylinder and is associated with said arm.

[0003] In known equipments of the type defined above, for example inpneumatic handling equipments, also called “tilter devices”, anomalousconditions of delivery of fluid under pressure to the chamber of thecylinder can take place, which may involve on the one hand risks to theintegrity of the structure of such equipments and of the equipmentassociated with them, and on the other hand risks to the safety ofoperators who may be close to the equipments.

[0004] These anomalous conditions are essentially of two kinds.

[0005] A first anomalous condition can take place in the case in which,for example after a maintenance operation carried out on the equipment,the feeding and exhaust lines of the fluid under pressure are notcorrectly connected to the opposite ends of the cylinder, in particularif an end of the cylinder is connected with the feeding of the fluidunder pressure while the other end freely communicates with the outerenvironment. When, in such conditions, the fluid under pressure is fedonly to one of the cylinder ends, the piston moves violently against thecylinder end which is in communication with the outer environment,causing the arm of the equipment to fall down sharply to anend-of-travel position.

[0006] Another anomalous condition occurs in the case of a pressure dropin the feeding line of the fluid under pressure to the cylinder, inparticular if the oscillation axis of the arm of the equipment is notarranged vertically and if the piston has not reached as yet theend-of-stroke position in which the toggle joint associated with the rodmakes irreversible its movement in the cylinder. In this case in fact,owing to the lack of a counter-pressure and under the weight of theapparatuses associated with the arm, it can fall down violently towardsits lower end-of-travel position.

[0007] In order to avoid the latter anomalous condition, devices forcontrolling the motion of the piston rod have been proposed, whichoperate on the basis of the principle to apply a friction force againstthe outside surface of the rod in the case of a pressure drop. Forexample, to this purpose braking devices may be used which includeplanes inclined with respect to the cylinder axis, to which rollers orballs are associated, which are intended to interfere with theperipheral surface of the rod when a pressure drop below a predeterminedthreshold occurs. Other braking devices employ a reed member having athrough circular hole in which the rod is inserted, whose diameter islittle greater than that of the rod. In the latter devices, in theoperation with the fluid fed under normal pressure, the sheet member isperpendicular to the axis of the rod, whereby the rod can slide axiallythrough it. In the case of pressure drop, the reed member is placed in aconfiguration inclined with respect to the rod axis, so that aninterference take place between the edges of its through hole and theradial surface of the rod, which causes the axial locking of the latter.

[0008] At any rate, the devices mentioned above for controlling themovement of the rod, and therefore the oscillation of the arm, may turnout to be not very practical or not very reliable in use. In fact, theiroperation can be affected by the dimensions of the mechanical membersinvolved in the operation, so that the wear of one of the members of thedevice can jeopardize their good operation, as well as the presence offoreign bodies, also if they are very small, in the fluid fed to thecylinder. Moreover, such devices allow to lock the rod when it is movingalong only one of its shifting directions, and require therefore to bedoubled when the locking of the motion of the rod in both its shiftingdirections is desired. In practice, if inclined planes with rollers orballs are used, it will be necessary to provide inclined planes withrespective rollers or balls for each of the shifting directions of therod, while if bored reed members are used for locking the rod, two reedmembers, one for each shifting direction of the rod, will have to beprovided.

[0009] In both the anomalous feeding conditions of the cylinderconsidered above, the traditional swingable lever handling equipmentsrisk to undergo serious damages which could jeopardize their operationand that of the apparatuses carried by their swingable arm, as well asto cause damages to possible people standing close to the equipments, ifthey are not equipped with devices adapted to prevent the arm to falldown in the event of an anomaly in the feeding of the fluid underpressure to the cylinder.

[0010] The main object of the present invention is therefore to providea dampening device intended to fit out a handling equipment of theswingable lever type, which is able to prevent that malfunctions mayoccur in the case in which the anomalous feeding conditions mentionedabove take place.

[0011] This object is attained thanks to the fact that an axial cavityseparated from the cylinder chamber and containing a service fluid isformed inside the rod, a stem rigidly connected with the cylinder andprovided with orifice means for the service fluid being sealingly andslidably mounted in such a cavity, so that the movement of the rod withrespect to the stem is slowed down as a consequence of the flowing ofthe service fluid through the orifice means, if the sliding speed of themain piston inside the cylinder exceeds a threshold speed set by thecross-section of the orifice means.

[0012] Thanks to these characteristics, the dampening device of theinvention is marked by a simple and compact structure allowing to obtainan effective slowing down of the arm towards the end-of-travelpositions, in the case in which an anomaly in the feeding of thecylinder takes place, keeping at the same time the hindrance and theweight of the equipment small, and allowing to limit its productioncosts.

[0013] Further characteristics and advantages of the invention willbecome more clearly evident from the reading of the detailed descriptionwhich follows, given purely by way of a non limiting example andreferred to the attached drawings, in which:

[0014]FIG. 1 is a schematic elevational side view of a swingable leverhandling equipment provided with a dampening device according to theinvention,

[0015]FIG. 2 is an enlarged cross-sectional view of a detail of theequipment indicated by the arrow II in FIG. 1, and

[0016]FIG. 3 is a view similar to FIG. 2, showing a different workingcondition of the device.

[0017] With reference to the FIG. 1 indicates as a whole a handlingequipment of the swingable lever type, which is operated by means offluid under pressure, typically air.

[0018] The equipment 1 comprises a body 3 to which a double acting fluidcylinder 5 is associated for driving a fork lever arm 7 by means of atoggle joint unit of a type known per se and not illustrated in thefigures, which is contained inside the body 3 of the equipment 1. Inbrief, the toggle joint unit allows to set in an oscillation motion apair of coaxial crank pins 11 on which the branches 13 of the fork arm 7are fitted, as from the reciprocating motion of a driving end 10 a of arod 10 which is slidable with respect to the cylinder 5. Then, anattachment plate 13 a is fastened to the branches 13, which is providedwith holes and/or openings in order to allow to connect apparatuses (notshown in the figures) to be moved by the equipment 1.

[0019] A main piston 15 which is connected to the rod 10, is slidablyand sealingly mounted by annular seals 16, inside a chamber 18 definedby the body of the cylinder 5. The two opposite faces of the piston 15have each an axial sleeve portion 15 a, 15 b, whose diameter is slightlywider than that of the rod 10.

[0020] The chamber 18 is axially defined by a pair of heads 20 a and 20b, respectively higher and lower with reference to the figures.Respective feeding and exhaust lines 21 a, 21 b and 22 a, 22 b for thefluid under pressure are formed in each of the heads 20 a and 20 b. Thelines 21 a and 21 b or 22 a and 22 b are selectively connected, by aswitching device of a type known per se, with a source of fluid underpressure, in order to produce alternatively over-pressure conditions onone of the faces of the piston 15, so as to cause the reciprocatingmotion of the piston 15 inside the chamber 18 between the heads 20 a and20 b. Each of the lines 21 a, 21 b has preferably a pair of branchlines, one of which ends in the chamber 18 facing a respective face ofthe piston 15, the other one ending into a seat 25 a, 25 b for receivinga respective sleeve portion 15 a, 15 b of the piston 15 when the pistonis in an end-of-stroke position.

[0021] In the rod 10 a cylindrical cavity 27 is formed axially, in whichan enlarged head 29 of a sliding stem 30 is slidably and sealinglymounted. The head 29 is provided with a peripheral seal 32 bearing onthe sidewall of the cavity 27. The end of the stem 30 opposite to thatsupporting the head 29 is rigidly connected to a support plate 34anchored to the bottom of the cylinder 5, for example by means of aplurality of axial screws (not illustrated in the figures).

[0022] The cavity 27 is filled up with a service fluid, typically oil,and is separated with respect to the outer environment in order toprevent the discharge of such a liquid. To this end, a bored plug 36which is screwed at the end of the rod 10 opposite to its driving end 10a, is arranged on the side of the chamber 18. The plug 36 is crossedcentrally by the stem 30, a ring-like seal 37 being interposed betweenthe stem 30 and the plug 36.

[0023] On the side of the rod 10 close to the drive end 10 a, anauxiliary piston 38 which will be considered in further detail in thefollowing, is inserted in the axial cavity 27. The piston 38 is providedwith a ring-like seal 39 similar to the seal 37 of the bored plug 36.

[0024] Moreover, the stem 30 is provided with orifice means for theservice fluid, which are conveniently arranged at its end provided withthe head 29. These orifice means can consist of a longitudinal hole 31opening at the end of the stem 30 facing the auxiliary piston 38 andconnected with a calibrated transversal hole 31 a opening on the side ofthe enlarged head 29 facing the plug 36.

[0025] As a result of the sliding of the piston 15 inside of the chamber18, and therefore of the rod 10 with respect to the head 20 a, theenlarged head 29 of the stem 30 slides inside the cylindrical cavity 27forcing the service fluid to flow through the orifice means constitutedby the holes 31 and 31 a, so as to pass from a side to the other of thehead 29. The hole having the smaller cross-section of the orifice means,that is the hole 31 a in the case illustrated in the figures but whichcould be otherwise the hole 31, is dimensioned in such a way that, inthe normal operation of the equipment 1, the rod does not undergo anyappreciable slowing down. However, its cross-section is such as toinvolve a slowing down of the rod 10 if the movement speed of the rodexceeds a prefixed threshold, owing to the viscous friction caused bythe passage of the service fluid through the holes 31 and 31 a. Inparticular, in the case in which a condition of anomaly of one of thekinds considered above in connection with the feeding of the cylinder 5,had to be taken place, the excessive movement speed of the rod 10 isslowed down owing to the passage of the service fluid through the holes31 and 31 a of the stem 30, which causes a dampening of the oscillationof the arm 13 of the equipment 1.

[0026] In the case in which, as illustrated in the figures, the changeof position of the enlarged head 29 inside the cavity 27 involves adifferent extension of the stem 30 inside such a cavity, it is necessaryto provide a device for compensating the longitudinal extension of thecavity 27, in view of the fact that the working volume for the servicefluid must remain constant. To this end, the auxiliary piston 38 ismounted floating in the cavity 27 and it can be associated with elasticthrust means 40, constituted by a coil spring, biasing it towards thestem 30. However, it has been surprisingly found that the spring 40 canbe eliminated without jeopardize the operation of the device, andconcurring to reduce the number of the parts of the equipment and,consequently, its total cost.

[0027] Moreover, the auxiliary piston 38 is associated with guide meansof its axial movement in the cavity 27, comprising a pin 42 an end ofwhich is fixed to the auxiliary piston 38, while the opposite end isslidable in a corresponding seat 46 formed in proximity of the drivingend 10 a of the rod 10. Preferably, the seat 46 communicates with theouter environment with respect to the cylinder 5, by means of a venthole 48.

[0028] In the case in which it is desirable to adjust the operatingthreshold of the dampening device, that is of the threshold speed of themain piston 15 beyond which its sliding within the chamber 18 has to beslowed down, adjusting means of the cross-section of the orifice meansin which the service fluid passes, can be arranged. For example, aspindle (not illustrated in the figures) can be arranged in a coaxialhole inside the stem 30 and associated with the base of the stem 30 inproximity of the plate 34 by means of a threaded connection, which has aconical tip at his end facing the driving end of the rod 10, in order tocooperate with a corresponding seat formed in a position adjacent to thehole 31, for allowing the section of the hole to be changed as a resultof the control of such a spindle by means of a tool which can be drivenfrom the outside of the cylinder 5.

1. A device for dampening the oscillation of the arm of a handlingequipment of the swingable lever type, which equipment (1) comprises adriving double acting cylinder (5) having a chamber (18) in which a mainpiston (15) is sealingly mounted, which is slidable as a result of theselective delivery of fluid under pressure at opposite zones of thechamber (18) of the cylinder (5), the main piston (15) being connectedto a rod (10) having a driving end (10 a) which projects from thecylinder (5) and is associated with said arm (7), characterised in thatan axial cavity (27) separated from the chamber (18) of the cylinder (5)and containing a service fluid is formed inside the rod (10), a stem(30) rigidly connected with the cylinder (5) and provided with orificemeans (31, 31 a) for the service fluid being sealingly and slidablymounted in such a cavity (27), so that the movement of the rod (10) withrespect to the stem (30) is slowed down as a consequence of the flowingof the service fluid through the orifice means (31, 31 a), if thesliding speed of the main piston (15) inside the cylinder (5) exceeds athreshold speed set by the cross-section of the orifice means (31, 31a).
 2. A device according to claim 1, characterised in that the stem(30) has an enlarged head (29) in proximity of which orifice means (31,31 a) for the service fluid are arranged.
 3. A device according to claim2, characterised in that a seal (32) is interposed between the enlargedhead (29) of the stem (30) and the wall delimiting the axial cavity (27)of the rod (30).
 4. A device according to anyone of claims 1 to 3,characterised in that the stem (30) has an end fixed to a support plate(34) anchored to the bottom of the cylinder (5).
 5. A device accordingto claim 1, characterised in that the axial cavity (27) of the rod (30)has a variable longitudinal extension for allowing to compensate thevariation of the extension of the stem (30) received inside the cavity(27).
 6. A device according to claim 5, characterised in that a floatingauxiliary piston (38) is arranged in proximity of the end of the axialcavity (27) opposed to the stem (30).
 7. A device according to claim 6,characterised in that the floating auxiliary piston (38) is associatedwith guide means (42, 46) for its axial movement.
 8. A device accordingto claim 7, characterised in that the guide means of the axial movementof the auxiliary piston (38) comprise a pin (42) one end of which isconnected to the auxiliary piston (38), while the opposite end isslidably mounted in a corresponding seat (46) formed in proximity of thedriving end (10 a) of the rod (10).
 9. A device according to claim 8,characterised in that said seat (46) communicates with the outerenvironment with respect to the cylinder (5) by means of a vent hole(48).
 10. A device according to claim 1, characterised in that thecross-section of the orifice means (31, 31 a) is variable as a result ofthe movement of an adjustment member which can be controlled from theoutside of the equipment (1).